CALGARY, Alberta, July 6 (Reuters) - Alberta regulators on Thursday charged Nexen Energy, a wholly-owned subsidiary of CNOOC Ltd, for a pipeline spill in July 2015 at the company's Long Lake oil sands facility that leaked around 31,500 barrels of bitumen emulsion.

The Alberta Energy Regulator laid four charges under the province's Environmental Protection and Enhancement Act and one charge under the Public Lands Act. (Reporting by Nia Williams; Editing by Andrew Hay)